Phantom carrier circuit



June l0, 1930. H, s. BLACK 1,762,754

PHANTOM CARRIER CIRCUIT Filed May l1, 1928 Arron/ver Patented June 10,1930 UNITED STATES PATENT OFFICE HAROLD S. BLACK, OF EAST ORANGE, NEVJERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK,N. Y., A CORPORATION OF NEW YORK PHANTOM CARRIER CIRCUIT Applicationfiled. May 11,

This invention relates to Wave transmis sion, and especially tophantoming multiplex systems, as for example carrier Wave signalingsystems.

Considering, for example, terminal apparatus for a pair of two-conductorlines each transmitting voice frequency Waves and carrier Waves, when itis desired to phantom the lines for either voice or carrier Waves, orboth, for instance in the general manner disclosed in the patents toAffel 1,582,112 and 1,582,113 and OLeary 1,582,073, all issued April 27,1926, it is desirable to avoid deleterious effectsin the phantom circuitor circuits due to inclusion therein of side circuit filters used forfrequency separation of the voice frequency waves and carrier frequencyWaves.

It is an object of the invention to avoid such deleterious effects Whileeconomizing apparatus for effecting frequency separation of thedifferent messages intended for the different signaling channels,respectively.

It is also an object to, at the same time, economize With respect to thenumber of phantom coils required.

In one specific aspect the invention is a multiplex Wave transmissionsystem having side circuits with side circuit low frequency groupingfilters and side circuit high frequency grouping ilters in the sidecircuits. and'having a phantom circuit for lov.T frequency Waves, and/ora phantom circuit for high frequency Waves derived from the sidecircuits at such points thereof that Waves pass through the lowfrequency phantom circuit Without passing through the side circuit loWfrequency grouping filters and/or Waves pass through the high frequencyphantom circuit Without passing through the side circuit high frequencygrouping filters. All of the filters mentioned may be of the usualconstruction, as may also any filters used in the phantom circuits toeffect frequency selection or separation of low frcquency and/or highfrequency Waves intended for the 10W frequency and/or high frequencyphantom circuits respectively. The use of side circuit filters andphantom circuit filters of usual construction tends 'to- 1928. SerialNo. 276,895.

Ward economy of filter apparatus, by facilitating an economical designof the individual filters.

The points in the side circuits at which the phantom circuits arederived may be at the junction of the transmission lines with the sidecircuit grouping filters. Thus, a given set of phantom coils may beemployed for both phantom circuits, since the, Wares intended for thephantom circuits are derived from the side circuits before frequencyseparation of the low frequency Waves and the high frequency wavesintended for the phantom circuits.

Other objects and aspects of the invention Will be apparent from thefollowing description and claims.

Fig. 1 is a diagram of a system embodying one form of the invention; and

Fig. 2 is a diagram of a system embodying another form of the invention.

Referring to Fig. 1, HFL and HFL represent tyvo telephone lines, eachcomprising a pair of conductors Which may be phantomed in a 'Well knownmanner so that each pair of conductors acting in parallel operates oneside of a phantom circuit. The phantom connections are established bymeans of transformers 10 and 10, from the middle points of whosewindings taps ll and 11 are led to form the phantom terminals of thesystem.

In order that the line HFL may be employed for carrier transmission, abranch CL, is provided which leads to carrier equipment of any type wellknown in the art, and in this branch a high pass filter 12 is iucluded.This high pass filter is of the broad band type which freely transmits aband of frequencies Within certain limits, While sharply attenuating andsuppressing the frequencies lying Without the limits of the band. Thefilter' is so designed as to pass the various carrier frequenciesemployed in the system together with their associated side bands, but itwill not permit ordinary voice currents transmitted over the line EFL topass into the circuit CL3. The ordinary voice currents transmitted overthe conductor HFL must be separated from the Cil vcarrier frequenciesand transmitted through cies are thereby prevented from entering thevoice side circuit VLB.

In a similar manner, the line HFL is provided with two branches, oneleading through the high pass filterV 14 to the side carrier circuit GLand the other leading through the low pass filter 15 to the voice sidecircuit VL.

The arrangement so far described is that ordinarily employed for-superposing a vplurality of carrier channels on an ordinary voicechannel. It is possible toY phantom a pair of circuits of this type forordinary voice transmission by meansof the phantom coils 10 and 10 withtheir phantom conductors 11 and 11. The voice currents transmitted overthe phantom, in so far as any unbalance occurs between the twoconductors ofthe side circuit, are prevented from entering the carriercircuit, such as the circuit CLS, by the high `pass filter. The effectupon the phantom of the filter LFS in the two conductors of the sidecircuit in introducing impedance due to the series coils y connection byintroducing` phantom coils,

such as 20 and 20" between the lines HFL and HFL and the high passfilters 12 and 14. Conductors 211 and 21 are led from the midpointsof`the phantom coils, as indicated, to form the phantoincarrier terminalCLI, which leads to suitable carrier equipment. With this arrangement,the Aphantom carrier currents need not be transmitted through theimpedance of any of the side circuit filters.

In order to provide 'the necessary frequency separation between thevoice currents transmitted over the phantom and the carrier currentstransmitted over the phantom, a low pass filter 16 is. included in thevoice phantom terminals VLP and a high class filter f1-7 vis included inthe carrier phantom terminal CLD. These lters, are similar to noisy orunbalanced line, and therefore serve to reduce .noise caused, forexample, by induction from power lines Vvinto lines HFL and HFL or bystatic7 picked up in thoser lines.

Condensers 23 connected between the halves of the line windings oftransformers 20, 20Y and 22, facili-tate transmission of ringingcurrents of, for example, 2Ol cycles or 133 cycles, from or to the linesHFL and HFL. c

Fig. 2 shows another form of the invention. Parts having the samereference characters in the two figures are identically alike instructure and function. The filters 12 to 15 of Fig. 2 are similar instructure and function to the filters .12 to, 15 respectively, of Fig.1, but may be of cheaper design, for reasons indicated hereinafter. n

Thus, the system of Fig. 2 comprises the lines HF L and HFL eachtransmitting voice and carrier frequencies, the side circuit lowfrequency grouping` filters 13 and 15, the side circuit high frequencygrouping filters .12 and 14', a phantom circuit VLp for low frequencywaves and a phantom circ uitCLp for carrier or high frequency waves.These phantom circuits are derivedV from the side circuits .at thejunctions of the transmission lines HFL and HFL with the side circuitgrouping filters, by employing phan, tom coils 30 and 30 for bothphantom circuits. The low frequency Waves and the carrier waves intendedto be transmitted from the transmission lines HFL and HFL to the phantomcircuits VLp and CLI, are derived from the transmission lines beforefrequency separation ofY the low frequency waves and the carrierfrequency waves; and Y these derived low frequencyV waves and carrierwaves are separa-ted by the filters 16 and 17. Y

Thus, the phantom circuits VLp and CLp are derived from the sidecircuits at the line sideof the side circuit grouping filters 12', 13',14 and 15, so that the phantom circuits do not include side circuitgrouping filters. Therefore, the deleterious effects which would resultfrom inclusion of such filters are avoided. Y c

The transformers 30 and 30, and transformer 33, reduce deleterious noiseeffects,

as noted of transformers 20, 20 and 23 in Fig. l.

ln Fig. 2, since the low frequency phantom path does not include the lowpass filters of the side circuits, any dissymmetry in those fnterscannotintroduce impedance in the low frequency phantom circuit. Therefore, thefilters 13 and l5 can be of cheaper design than the filters 13 and l5.Further, under conditions usual in practice, inclusion of low passfilters of side circuits in low frequency phantom paths introducessuiiicient impedance to cause objectionable distortion or degradation ofsignal quality, and moreover, upset the impedance balance between thevoice phantom circuit VLl, and its balancing network at the voicephantom circuit repeater hybrid coil or bridge transformer. (T herepeater with the hybrid coil and the balancing network are not shown inthe drawing, as it will be understood that it can be connected to thevoice phantom circuit in the usual way).

In both figures of the drawing, all of the filters can be of the usualconstruction.

TWhat is claimed is:

l. A multiplex wave transmission system comprising side circuits, sidecircuit low frequency grouping filters and side circuit high frequencygrouping filters in the side circuits, and a phantom circuit derivedfrom the side circuits at such points thereof with relation to said sidecircuit filters that Waves transmitted over said side circuits passthrough the phantom circuit without passing through either side circuitfilter.

2. A multiplex wave transmission system comprising side circuits, sidecircuit low frequency grouping filters and side circuit high frequencygrouping filters in said side circuits, a phantom circuit for lowfrequency waves, and a phantom circuit for high frequency waves, bothderived from said side circuits at such points thereof with relation tosaid side circuit filters that waves intended for said phantom circuitsleave the side circuits before Afrecpuency separation of the lowfrequency waves and the high frequency waves intended for the phantomcircuits.

3. A multiplex wave 'transmission system comprising side circuits, sidecircuit low frequency grouping filters and side circuit high freiluencygrouping filters in the side circuits, and a phantom circuit derivedfrom the side circuits at such points thereof with relation to saidfilters that the impedance of neither filter 'is included in the phantomcircuit, each of said filters comprising` series and shunt paths, andcertain of said shunt paths consisting of ay single reactance element.

4. A system comprising two side circuits and a phantom circuit derivedtherefrom, said side circuits including` transmission lines and physicalpaths selective of waves of a given frequency range, one of said pathshaving one end connected to one of said lines, and the other of saidpaths having one end connected to the other of said lines, said systemalso comprising, in addition to said side circuits and a voice wavephanton'i circuit derived therefrom, said side circuits including voicewave transmission lines and voice wave physical paths selective of wavesof given characteristics, one of said paths having one end connected toone of said lines, and the other of said paths having one end connectedto the other of said lines, said system also comprising, in addition tosaid side circuit selective paths, a physical path for voice waves,included in said phantom circuit and selective of waves of givencharacteristics and connected to said ends of said side circuitselective paths, so that the latter paths are not included in saidphantom circuit.

6. A system comprising two carrier wave side circuits and a carrier wavephantom circuit derived therefrom, said side circuits including carrierwave transmission lines and carrier wave physical paths selective ofwaves of Given characteristics, one of said paths having one endconnected to one of said lines, and the other of said paths having oneend connected to the other of said lines, said system also comprising,in addition to said side circuit selective paths, a physical path forcarrier waves, included in said phantom circuit and selective of wavesof given characteristics and connected to said ends of said side circuitselective paths, so that the latter paths are not included in saidphantom circuit.

i. A system comprising two signal transmission lines each adapted totransmit voice waves and carrier waves, a voice wave sine circuitincluding one of said lines, a voice wave side circuit including theother of said lines, a voice wave phantom circuit derived from saidlines, and a carrier wave phantom circuit derived from said lines, saidvoice wave side circuits including voice wave physical paths selectiveof waves of given characteristics, one of said voice wave paths havingone end connected to one of said lines, and the other of said voice wavepaths having one end connected to the other of said lines, said systemalso comprising, in addition to said side circuit voice wave selectivepaths, a physical path for voice waves, included in said voice wavephantom Uli ite

vso

circuit and selective of waves of given characteristics and connected tosaid ends of said side .circuit voice wave fselective paths so that thelatter paths are not included in said voice wave phantom circuit, saidcarrier wave side circuits including carrier wave physical pathsselective of waves of given characteristics, one of said carrier wavepaths having one end connected to vone of said lines, and the other ofsaid carrier wave paths having one end connected to the other of saidlines, said system also comprising, in addition to said side circuitcarrier wave selective paths, a physical path for carrier waves,included in said carrier wave phantom circuit and selective of waves ofgiven characteristics and connected to'said ends of saidV side circuit'carrier wave selective paths, so that the latter paths are not includedin said carrier wave phantom circuit.

8. The method which comprises transmitting different messages ofdifferent frequency ranges respectively over one path, transmittingdifferent messages of different frequency ranges respectively over asecond path, transmitting messages over said two paths in parallel,deriving from the two paths said messages transmitted over the two pathsin parallel, to the exclusion of said other messages, and thereaftereffecting frequency separation of said messages of different frequencyranges transmitted over the one path'and frequency separation ofjsaidmessages of different frequency ranges transmitted over the second path.

9. The method which comprises transmitting different messages ofdifferent frequency ranges respectively over one path, transmittingdierent messages of different frequency ranges respectively over asecond path, transmitting different messages of different frequencyranges, respectively, over the two paths in parallel, deriving from thetwo paths said messages transmitted over the two paths in parallel, tothe exclusion of said other messages, and thereafter effecting frequencyseparation of said niessages of different frequency ranges transmittedover the two paths in parallel, frequency separation of said messages ofdifferent frequency ranges transmitted over the one path, and frequencyseparation of said messages of different frequency ranges transmittedover the second path.

In witness whereof, I hereunto subscribe my name this 10th day ofMay,1928.

HAROLD S. BLACK.

